1. Field of the Invention
This invention relates to a backrest for a seat in general, and more particularly to a seat backrest constructed to resiliently yield in substantial conformity with the body contour of an occupant of the seat.
2. Description of the Related Art
Many different seat backrests have been proposed in the art for increasing the comfort of a seated occupant. As shown, for example, in German Patent DE-41 37 488.6, the backrest may have a movable part that engages a lower region of the back of the occupant, thereby helping to alleviate back discomfort during long seating. Although generally satisfactory for its intended purpose, experience has shown that the known backrests with movable parts are subject to material fatigue and breakage over time, thereby rendering them unusable.
On the other hand, there is also known, from the U.S. Pat. No. 4,799,732 to Yamazaki, a chair seat inclining and moving device in which the backrest proper is subdivided into two parts one of which includes two side portions delimiting a recess between themselves, while the other has a projection substantially conformingly projecting into the recess in an initial or rest position of the backrest. The two parts are connected to one another for pivoting and acted upon by respective springs urging the movable part towards its rest position when the seat is not occupied.
However, when an occupant sits down on the seat and reclines back ever so slightly in contact with the backrest, the forces exerted by his or her back on the backrest cause the movable part to pivot relative to the other part, offering resilient resistance in the process, which is supposed to be perceived as comfort. Yet, the solution presented in this patent is based on the erroneous premise that the magnitude of the step that comes into being between the stationary and movable parts as the latter is being pushed back needs to be kept to a minimum; as a consequence, the pivoting axis bisects the recess and the projecting portion extending into it about half-way down. That, of course, means that the step will be situated somewhere at the mid-back region of the user, i.e. at a location at which it will be perceived as an unwelcome disturbance, no matter how small it may be, thus defeating the very purpose of this patent.
To complete the picture, it is also to be pointed out that German patent 38 26 290.8-09 also discloses a backrest of a sitting piece of furniture, wherein either the central upper region of the upper backrest part and the central lower region of the lower backrest part exhibit greater elasticity than the remaining regions of the backrest, or both of these regions are rearwardly buckled. In this respect, it is to be mentioned that the increased elasticity of these two regions was achieved there by making the upper portion and the lower portion of bifurcated configurations, and by training respective stretched elastic belts around the prongs of such bifurcated portions so as to extend between the such portions.